Method of manufacturing outer tube of injector

ABSTRACT

The present invention provides a manufacturing method for manufacturing an outer tube of an injector having a barrel portion having an excellent circularity, while preventing generation of distortion or warp. A molten resin is injected into a cavity  17  of a metal mold  11  including: a fixed mold  13  having a hole portion  12  having a shape along the outer shape of the injector outer tube  1 ; a movable mold  14  closing the hole portion  12 ; and a core  15  inserted into the hole portion  12 . A cylindrical vacant portion is provided communicating with a flange forming portion  20  of the hole portion  12 . The molten resin R is injected from a sprue  22  and a runner  23  via a submarine gate  24  into the cylindrical vacant portion  21  and the molten resin R is introduced into the cavity  17 . The cylindrical vacant portion  21  has a push pin  25 . When the molten resin has become half-molten state, the resin in the cylindrical vacant portion is introduced with pressure into the cavity  17  by the push pin  25 . When the amount of the molten resin R in the cavity  17  is insufficient, a wait position of the push pin is moved in a direction apart from the connection portion of the submarine gate  24 , so as to inject the molten resin R and supplement the insufficient resin in the cavity  17.

[0001] This application is the national phase under 35 U.S.C. §371 ofPCT International Application No. PCT/JP02/05833 which has anInternational filing date of Jun. 12, 2002, which designated the UnitedStates of America.

TECHNICAL FIELD

[0002] The present invention relates to a method for manufacturing anouter tube of an injector made from a synthetic resin.

BACKGROUND ART

[0003] Conventionally, there are known disposable injector outer tubesproduced by injection molding of a synthetic resin such aspolypropylene, polycarbonate, and polymethylpentene (TPX). Thesesynthetic resins are inactive for a medicine liquid. The polycarbonateand TPX have an advantage that they can be sterilized by a high-pressurevapor and have a high transparency.

[0004] As shown in FIG. 1, the injector outer tube 1 has a barrelportion 2, a lure-tapered portion 3 arranged at a front end of thebarrel portion 2, and a flange portion at a rear end of the barrelportion 2 for holding by fingers. The injector outer tube 1 is normallyproduced by injection molding by using a metal mold 11 consisting of afixed mold 13, a movable mold 14, and a core pin (core) 15.

[0005] The fixed mold 13 has a hole portion 12 having a shape of theouter shape of the injector outer tube 1. The hole portion 12 isprovided vertically on a parting line 16 with the movable mold 14.Moreover, the core pin 15 is adapted to pierce the movable mold 14 to beinserted into the hole portion 12. Furthermore, a molten resin isinjected into a cavity 17 formed by the hole portion 12, the movablemold 14, and the core pin 15. The cavity 17 consists of a barrel formingportion 18 and a lure-taper forming portion 19 formed by the core pin 15inserted into the hole 12 and a flange forming portion 20 formed betweenthe hole portion 12 and the movable mold 14.

[0006] It should be noted that in the metal mold 11, the fixed mold 13has a sprue, a runner, and a gate (not depicted) for guiding a moltenresin to the cavity 17.

[0007] Injection of a molten resin into the cavity 17 is performed asfollows, for example. As shown in FIG. 7A, a plurality (three in thefigure) of chip gates 31 are arranged at the front end of the barrelforming portion 18; as shown in FIG. 7B, a plurality (two in the figure)of chip gates 31 are arranged at the base of the lure-taper formingportion 19; or as shown in FIG. 7C, a plurality (two in the figure) ofpin point gates 31 are arranged at the front end of the barrel formingportion 18. It should be noted in FIG. 7A to FIG. 7C, for explanation,the barrel forming portion 18, the lure-taper forming portion 19, therunner 23, and the gate 31 arranged inside the fixed mold are exposed.

[0008] By using the method of FIG. 7A to FIG. 7C, it is possible toobtain a metal molded product without performing cutting the gate 31after injection of the molten resin.

[0009] However, when the methods of FIG. 7A to FIG. 7C are used, theresin is supplied from the front end side of the core pin 14 into thecavity 17 under a high pressure and accordingly, there is a problem thatthe core pin 15 is inclined, making the thickness of the barrel portion2 uneven. Moreover, when the resin portions injected from the pluralityof gates 31 join in the cavity 17, a distortion may be caused,deteriorating the circularity of the cross section of the barrel portion2.

[0010] Instead of the methods of FIG. 7A to FIG. 7C, there is also amethod to provide only one gate 31 at the rear end side of the barrelforming portion 18 as shown in FIG. 8. According to the method of FIG.7, there is no confluence of the injected resin in the cavity 17, andhence it is possible to prevent the aforementioned distortion.

[0011] However, in the method of FIG. 8, when the resin filled in thecavity proceeds along the core pin 15, the flow front F of the resinproceeds earlier at the side where the gate 31 is provided and the flowfront F is delayed at the opposite side of the gate 31. For this, asshown in FIG. 9, in the injector outer tube 1 obtained by the method ofFIG. 8, the barrel portion 2 has a thicker wall at the side where thegate 31 is provided, which deteriorates the circularity of the crosssection of the barrel portion and warp is caused.

[0012] Moreover, the injector outer tube 1 is used in combination with aplunger (not depicted) sliding along the inner wall of the barrelportion 2. When the plunger has a gasket made from a thermoplasticelastomer, if the circularity is low, the gasket is creep-deformed,causing a problem that a liquid may leak when the injector is used.

DISCLOSURE OF THE INVENTION

[0013] It is therefore an object of the present invention to provide amanufacturing method of an outer tube of an injector capable ofmanufacturing an outer tube of an injector having a barrel portion ofuniform thickness and an excellent circularity and preventing generationof distortion or warp.

[0014] In order to achieve the aforementioned object, the presentinvention provides a manufacturing method of an outer tube of aninjector comprising the step of molding an outer tube of an injector byinjecting a molten resin into a cavity defined by a metal moldcomprising: a fixed mold having a hole portion having a shape along anouter shape of the injector outer tube consisting of a barrel portion, ataper portion arranged at a front end of the barrel where an injectionneedle is mounted, and a flange portion arranged at a rear end of thebarrel, the fixed mold being provided vertical to a parting line definedby a rear end of the flange portion forming portion; a movable mold forclosing the hole portion along the parting line; and a core piercing themovable mold and inserted into the hole portion, wherein the fixed moldincludes a sprue for guiding the molten resin and a runner branchingfrom the sprue; the movable mold includes a cylindrical vacant portionarranged vertical to the parting line and communicating with a portionwhere the flange portion is formed, and a submarine gate communicatingwith the runner and connected to an intermediate portion of thecylindrical vacant portion; and the molten resin is injected from thesprue via the runner and the submarine gate into the cylindrical vacantportion and introduced via the cylindrical vacant portion into thecavity.

[0015] According to the manufacturing method of the present invention, acavity having a shape of the injector outer tube is formed by the holeportion of the fixed mold, the movable mold closing the hole portion,and the core piercing the movable mold and is inserted into the holeportion. The cavity has a space between the hole portion and the corefor forming a barrel portion of the injector outer tube and a portionfor forming a barrel front end portion at the front end of the barrelportion. Moreover, the cavity has a portion between the hole portion ofthe rear end of the barrel portion and the movable mold for forming athe flange portion. The portion for forming the flange portioncommunicates with the cylindrical vacant portion arranged in the movablemold.

[0016] When a molten resin is injected from the sprue via the runner andthe submarine gate, the molten resin is firstly injected into thecylindrical vacant portion and then introduced from the cylindricalvacant portion into the portion for forming the flange portion. Afterfilling the portion for forming the flange portion, the molten resin isintroduced into a portion for forming the injector outer tube and flowsfrom the portion for forming the flange portion into the portion forforming the barrel front end portion.

[0017] As has been described above, the molten resin is introduced intothe barrel portion for forming the injector outer tube after filling theportion for forming the flange portion and accordingly, the flow frontof the resin flows uniformly along the circumferential direction of thebarrel portion. This makes a uniform wall thickness of the barrelportion and prevents generation of warping.

[0018] Moreover, since the molten resin is introduced into the cavityonly from the cylindrical vacant portion, there is no confluence withthe molten resin introduced from the other portion. Thus, it is possibleto prevent generation of distortion caused by confluence.

[0019] Moreover, the manufacturing method according the presentinvention is characterized in that the metal mold includes a push pinprovided slidably along an inner wall of the cylindrical vacant portionand having a tip end which can proceed up to the parting line; themolten resin is injected when the push pin is waiting at a predeterminedwait position which is at opposite side of the fixed mold with respectto a connection portion of the submarine gate; and when the molten resinhas become half-molten state, the push pin is made to proceed up to theparting line so as to introduce the molten resin with pressure from thecylindrical vacant portion into the cavity.

[0020] According to the manufacturing method of the present invention,when the molten resin has become half-molten state, the push pin is madeto proceed up to the parting line and the resin is introduced withpressure from the cylindrical vacant portion into the cavity.Accordingly, when removing the metal molded injector outer tube from themetal mold, there is no case that the flange portion is connected to aresin solidified in the cylindrical vacant portion. This can eliminatethe process of cutting a resin solidified in the cylindrical vacantportion. Moreover, it is possible to make smooth the portion where theflange is connected to the cylindrical vacant portion.

[0021] Moreover, by introducing with pressure the resin from thecylindrical vacant portion into the cavity, it is possible to supplementthe resin amount filled in the cavity, which in turn prevents generationof a vacant portion in the resin. Thus, it is possible to obtain anouter tube of an injector of a complete shape.

[0022] It should be noted that the timing to advance the push pin may beany time after the molten resin is injected and before the resin issolidified.

[0023] Moreover, there is a metal mold that the molten resin filled inthe cavity is always insufficient regardless of the injection condition.In such a case, conventionally, the sprue and the runner are cut off toincrease the path of the molten resin, thereby solving the problem ofinsufficient molten resin. However, when the cutting off is too much, itis difficult to repair again and the metal mold itself should beabandoned as a defective product.

[0024] In the manufacturing method of the present invention, when themolten resin has become insufficient in the cavity even after the resinin the cylindrical vacant portion is introduced with pressure into thecavity using the push pin, the wait position of the push pin is modifiedin a direction apart from the connection portion of the submarine gate,so as to inject the molten resin, thereby compensating the insufficientresin in the cavity. Modification of the wait position of the push pinmay be performed by mechanically retreating the push pin in a directionapart from the connection portion of the submarine gate or by cuttingoff the tip end of the push pin.

[0025] Accordingly, there is no need of repairing the sprue and therunner by cutting, and it is possible to easily repair the metal moldcausing insufficiency of the molten resin to be filled. And this canprevent a case that the metal mold itself is abandoned as a defectiveproduct. It should be noted that when cutting off the tip end of thepush pin, even if the cutting off results in an excessive amount, thepush pin alone need be abandoned as a defective product. As compared tothe case that the entire metal mold is abandoned as a defective product,the loss is small even if the repair fails.

[0026] Moreover, the manufacturing method according the presentinvention may be such that the metal mold has: a plurality of holeportions provided in the fixed mold; a plurality of cylindrical vacantportions provided in the movable mold closing the respective holeportions along the parting line and communicating with portions wherethe flange portions of the respective hole portions are formed; and aplurality of cavities defined by the cores piercing the movable moldsand are introduced into the respective hole portions, the fixed mold hasa sprue for guiding the molten resin and a plurality of runnersbranching from the sprue, the movable mold has a plurality of submarinegates communicating with the respective runners and connected to anintermediate portion of the respective cylindrical vacant portions, andthe molten resin is injected from the sprue via the runners and thesubmarine gates into the respective cylindrical vacant portions and viathe cylindrical vacant portions into the respective cavities. Accordingto the aforementioned mold, a plurality of injector outer tubes ofinjectors can be simultaneously obtained by injecting a molten resinfrom the sprue via the respective runners and submarine gates into therespective cylindrical vacant portions.

[0027] When simultaneously producing a plurality of injector outertubes, the molten resin amount may be insufficient in a particularcavity among the plurality of cavities. In this case, according to themanufacturing method of the present invention, for the cavity causing aninsufficient molten resin amount, as has been described above, the waitposition of the push pin is changed in a direction apart from theconnection portion of the submarine gate so as to inject the moltenresin and to thereby supplement the insufficient resin in the cavity.

[0028] In the manufacturing method according to the present invention,the molten resin may be one selected from a group consisting ofpolypropylene, polycarbonate, and polymethylpentene.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a perspective view showing a configuration example of anouter tube of an injector obtained by the manufacturing method of thepresent invention.

[0030]FIG. 2 is a cross sectional view explaining an example of themanufacturing method of the present invention.

[0031]FIG. 3 is a cross sectional view explaining a partially moldedproduct of the injector outer tube obtained by the manufacturing methodof the present invention.

[0032]FIG. 4 is a cross sectional view about IV-IV of FIG. 3.

[0033]FIG. 5 is a cross sectional view explaining an example of themanufacturing method of the present invention.

[0034]FIG. 6 is a cross sectional view explaining a conventionalmanufacturing method.

[0035]FIG. 7 is a perspective view showing gate arrangement in theconventional manufacturing method.

[0036]FIG. 8 is a cross sectional view explaining another gatearrangement in the conventional manufacturing method.

[0037]FIG. 9 is a cross sectional view explaining a barrel portion ofthe injector outer tube obtained by the conventional manufacturingmethod.

BEST MODE FOR CARRYING OUT THE INVENTION

[0038] The present embodiment is for manufacturing an injector outertube 1 shown in FIG. 1. The injector outer tube 1 is made from, forexample, polypropylene and has a lure-taper portion 3 at the front endof a cylinder-shaped barrel portion 2 where a injection needle ismounted and a flange portion 4 at the rear end of the barrel portion 2for holding by fingers. The flange portion 4 has an elliptical shapehaving a concave portion 5 made by taking out meat on the surfaceopposite to the barrel portion 2 and an injection trace (not depicted).

[0039] In this embodiment, the injector outer tube 1 is produced byusing a metal mold 11 shown in FIG. 2A. The metal mold 11 consists of afixed mold 13 having a hole portion 12 having a shape along the outershape of the injector outer tube 1, a movable mold 14 for closing thehole 12, and a core pin (core) 15 to be inserted through the movablemold 14 into the hole portion 12. The hole portion 12 is providedvertical to a parting line 16 and the movable mold 114 is arranged so asto close the hole portion 12 along the parting line 16.

[0040] By the metal mold 11, the hole portion 12, the movable mold 14,and the core pin 15 constitute a cavity 17 having the shape of theinjector outer tube 1. The cavity 17 has a barrel forming portion 18between the hole portion 12 and the core pin 15 and has a lure-taperforming portion 19 at the front end of the barrel forming portion 18 anda flange forming portion 20 at the rear end of the barrel formingportion 18. The barrel forming portion 18, the lure-taper formingportion 19, and the flange forming portion 20 correspond to the barrelportion 2, the lure-taper portion 3, and the flange portion 4 shown inFIG. 1, respectively.

[0041] Moreover, the movable mold 14 has a cylindrical vacant portion 21communicating with the flange forming portion 20 and a submarine gate 24connected to an intermediate portion of the cylindrical vacant portion21. The cylindrical vacant portion 21 is provided vertical to theparting line 16 and has a push pin 25 to introduce with pressure theresin filled inside into the cavity 17. The push pin 25 waits at apredetermined wait position in the cylindrical vacant portion 21opposite to the fixed mold with respect to the connection portion of thesubmarine gate 24.

[0042] Moreover, the fixed mold 13 has a sprue 22 for guiding the moltenresin injected from an injection apparatus (not depicted) and a runner23 branching from the sprue 22. The runner 23 communicates with thesubmarine gate 24. The submarine gate 24 extend below the connectionportion with the runner 23 by 45 degrees and is connected to theintermediate portion of the cylindrical vacant portion 21.

[0043] When producing the injector outer tube 1 by using the metal mold11, firstly, the hole portion 12 of the fixed mold 13 is closed by themovable mold 14 and the core pin 15 is inserted into the hole portion12, thereby forming the aforementioned cavity 17.

[0044] Next, a molten resin R injected from an injection apparatus (notdepicted) is introduced via the sprue 22, the runner 23, and thesubmarine gate 24 into the cylindrical vacant portion 21. The moltenresin R introduced into the cylindrical vacant portion 21 is thenintroduced into the flange forming portion 20 and after filling theflange forming portion 20, flows into the barrel forming portion 18.

[0045] The molten resin R is introduced into the barrel forming portion18 after filling the flange forming portion. Accordingly, like apartially molded product 1 a of the injector outer tube 1 shown in FIG.3, the flow front F can be formed almost uniformly along thecircumference of the barrel forming portion 18. It should be noted thatthe partially molded product 1 a of FIG. 3 is formed by intentionallyreducing the amount of the molten resin R introduced into the cavity 17in the metal mold 11 shown in FIG. 2A. As a result, as shown in FIG. 4,the barrel portion 2 has almost uniform wall thickness along thecircumference of the barrel portion 2.

[0046] Here, it is preferable that the cylindrical vacant portion 21 donot interfere with the core pint 1, so that the molten resin R isuniformly introduced into the barrel forming portion 18. For this, thecylindrical vacant portion 21 is arranged so as to communicate with theflange forming portion 20 at a position as far as possible from thebarrel forming portion 18.

[0047] When the cavity 17 and the cylindrical vacant portion 21 arefilled with the molten resin R as has been described above and themolten resin R is solidified, a boss is formed on the surface of theflange portion 4 opposite to the barrel portion 2 by the molten resin Rfilled in the cylindrical vacant portion 21 by the molten resin R filledin the cylindrical vacant portion 21. The flange portion 4 is used forholding by fingers when sliding a plunger (not depicted) along the innerwall of the injector outer tube 1 and presence of the boss hinders theoperation.

[0048] To cope with this, the boss can be cut off when the metal moldedinjector outer tube is removed from the metal mold. However, accordingto the present embodiment, when the molten resin R has becomehalf-molten state, as shown in FIG. 2B, the push pin 25 provided in thecylindrical vacant portion 21 and is normally waiting at theaforementioned wait position is made to proceed toward the fixed mold 13until it reaches the parting line 16. This makes the resin in thecylindrical vacant portion 21 be introduced with pressure into thecavity 17. In the injector outer tube 1 thus molded, only an injectiontrace (not depicted) remains on the surface of the flange portion 4opposite to the barrel portion 2 and the aforementioned boss is notformed, thereby obtaining a smooth surface. Moreover, when the push pin25 is made to proceed so as to introduce with pressure the resin fromthe cylindrical vacant portion 21 into the cavity 17, it is possible toobtain an effect to prevent formation of a vacant portion due to theinsufficient resin.

[0049] Moreover, as shown in FIG. 5, the metal mold 11 may have thefixed mold 13 having a plurality of hole portions 12; the movable mold14 having a plurality of cylindrical vacant portions 21 communicatingwith the flange forming portions 20 of the respective hole portions 12;and a plurality of core pins 15 to be inserted into the respective holes112, thereby forming a plurality of cavities 17. In this case, themovable mold 14 has a plurality of submarine gates 24 connected to theintermediate portion of the respective cylindrical vacant portions 21.Moreover, the fixed mold 11 has the sprue 22 for introducing the moltenresin R and a plurality of runners 23 branching from the sprue 22 tocommunicate with the respective submarine gates 24.

[0050] The molten resin R is injected from the sprue 22 via the runners23 and the submarine gates 24 into the respective cylindrical vacantportions 21 and into the cavities 17, thereby simultaneously obtaining aplurality of injector outer tubes 1.

[0051] In the metal mold for simultaneously producing a plurality ofinjector outer tubes 1, there is a case that the molten resin R isinsufficient in a particular cavity 17 among the plurality of cavities.To cope with this, in the manufacturing method according to the presentembodiment, for the cavity where the molten resin R becomesinsufficient, the wait position of the push pin 25 is modified apartfrom the connection portion of the submarine gate 24 when performinginjection of the molten resin R. Thus, for the amount of retreat of thewait position of the push pin 25 with respect to the fixed mold 13, themore molten resin R is introduced into the cylindrical vacant portion21. Accordingly, when the push pin 25 is made to proceed toward thefixed mold 13 to reach the parting line, the amount of the resinintroduced with pressure into the cavity 17 is increased, therebycompensating the insufficient resin in that cavity. It should be notedthat the cavity 17 where the molten resin R becomes insufficient can beexperimentally known after production of the metal mold 11 and actuallyperforming an injection molding of the injector outer tube 1.

[0052] It should be noted that FIG. 5 shows the metal mold 11 having twocavities 17 arranged at right and left of the sprue 22 but the number ofcavities may be more than two. In this case, a plurality of cavities maybe provided radially around the sprue 22.

[0053] Next, an example will be detailed.

EXAMPLE

[0054] In this example, as shown in FIG. 2A, by using the metal mold 11having one hole portion 12 and one core pin 15, an injector outer tubeof 1 having a barrel portion 2 of about 70 mm, of nominal size 5 mL, wasproduced. In the movable mold 14 of the metal mold 11, the cylindricalvacant portion had a diameter 3 mm and a length 5 mm.

[0055] In this example, by using motor injection apparatus (notdepicted), polypropylene of melt flow index (MFI) 20 to 30 at thecylinder temperature of 180 to 230° was injected from the sprue 22 viathe runner 23, the submarine gate 24 into the cylindrical vacant portion21 and into the cavity 17. In the apparatus of FIG. 2A, the sprue 22 isfairly long and there is a fear of increase of pressure loss of themolten resin R flowing. However, this increase of the pressure loss canbe prevented by providing a long nozzle in the injector apparatus orproviding heating means in the fixed mold 13 to obtain a hot sprue.

[0056] Moreover, the push pin 25 was operated by controlling theinjection delay between 0.2 to 2 seconds while monitoring the injectiontime by the pre-ejector function of the motor injection apparatus.

[0057] As a result, it was possible to obtain an injector outer tube 1having a preferable outer view at barrel portion 2 and the lure-taperportion 3. The injector outer tube obtained in this example wasevaluated by a circularity measurement apparatus and it was found thatas compared to a conventional injector outer tube, the circularity washigh and the cylindricality was preferable. Moreover, the injectiontrace was almost identical to an injection trace of a push pin used inan ordinary injection molding. There was no cloudiness or gate refuseand it was possible to form a smooth surface of the flange portion 4opposite to the barrel portion.

[0058] It should be noted that in this example, the injector outer tube1 was molded by polypropylene. However, when a further transparency andresistance for high temperature sterilization are required, it ispossible to mold by using a synthetic resin such as polycarbonate andpolymethylpentene (TPX).

[0059] Moreover, instead of the submarine gate 24 opening to thecylindrical vacant portion 21 in this example, it is possible to use asubmarine gate opening to the side surface of the flange forming portion20 or a pin gate opening to the side of the barrel forming portion 18 ofthe flange forming portion 20. However, the flange portion 4 shouldsatisfy the standard of the thickness and shape for suppressing rollingand capability to be connected to a syringe pump. The thickness shouldbe below 3 mm or not greater than 3.5 mm as is defined by ISO7886-2“Sterile hypodermic syringes for single use Part 2”. Which of theaforementioned thickness is employed is determined by the size of theinjector. For example, for the injector of nominal size of 5 mL in thisexample, the thickness of the flange portion should be below 3 mm.

[0060] As a result, when forming the flange portion of theaforementioned thickness, it becomes difficult from the metal moldstructure to employ the submarine gate opening to the side surface ofthe flange forming portion 20 or the pin gate opening to the side of thebarrel forming portion 20 of the flange forming portion 20.

[0061] Moreover, when employing the side gate for introducing the moltenresin R from the side surface of the flange forming portion 18, therunner should be cut off from the metal molded injector outer tube at alater step. In the case of a U-shape arranged banana gate forintroducing the molten resin R from the side of the movable mold 14 ofthe flange forming portion 18, the gate burr often remains and the gatecutting surface is not preferable.

INDUSTRIAL APPLICABILITY

[0062] The present invention can be used for a disposable injector usedas a medical instrument.

1. A method for manufacturing an outer tube of an injector, comprisingthe step of injecting a molten resin into a cavity defined by a metalmold comprising: a fixed mold having a hole portion having a shape alongan outer shape of the injector outer tube consisting of a barrelportion, a taper portion arranged at a front end of the barrel where aninjection needle is mounted, and a flange portion arranged at a rear endof the barrel, the fixed mold being provided vertical to a parting linedefined by a rear end of the flange portion forming portion; a movablemold for closing the hole portion along the parting line; and a corepiercing the movable mold and inserted into the hole portion, whereinthe fixed mold includes a sprue for guiding the molten resin and arunner branching from the sprue; the movable mold includes a cylindricalvacant portion arranged vertical to the parting line and communicatingwith a portion where the flange portion is formed, and a submarine gatecommunicating with the runner and connected to an intermediate portionof the cylindrical vacant portion; and the molten resin is injected fromthe sprue via the runner and the submarine gate into the cylindricalvacant portion and introduced via the cylindrical vacant portion intothe cavity.
 2. The method according to claim 1, wherein the metal moldincludes a push pin provided slidably along an inner wall of thecylindrical vacant portion and having a tip end which can proceed up tothe parting line; the molten resin is injected when the push pin iswaiting at a predetermined wait position which is at opposite side ofthe fixed mold with respect to a connection portion of the submarinegate; and when the molten resin has become half-molten state, the pushpin is made to proceed up to the parting line so as to introduce themolten resin with pressure from the cylindrical vacant portion into thecavity.
 3. The method according to claim 2, wherein when the moltenresin has become insufficient in the cavity, the wait position of thepush pin is modified in a direction apart from the connection portion ofthe submarine gate, so as to inject the molten resin, therebycompensating the insufficient resin in the cavity.
 4. The methodaccording to any one of claims 1 to 3, wherein the metal mold has: aplurality of hole portions provided in the fixed mold; a plurality ofcylindrical vacant portions provided in the movable mold closing therespective hole portions along the parting line and communicating withportions where the flange portions of the respective hole portions areformed; and a plurality of cavities defined by the cores piercing themovable molds and are introduced into the respective hole portions, thefixed mold has a sprue for guiding the molten resin and a plurality ofrunners branching from the sprue, the movable mold has a plurality ofsubmarine gates communicating with the respective runners and connectedto an intermediate portion of the respective cylindrical vacantportions, and the molten resin is injected from the sprue via therunners and the submarine gates into the respective cylindrical vacantportions and via the cylindrical vacant portions into the respectivecavities.
 5. The method according to any one of claims 1 to 4, whereinthe molten resin is one selected from a group consisting ofpolypropylene, polycarbonate, and polymethylpentene.